[ET-VK][ez] Explicitly skip marking output nodes that are mutable buffers

## Changes

* Move the logic skipping output nodes that are mutable buffers from runtime to AOT

## Context

A `fx.Graph` may return nodes that are mutable buffers:


```
    class GraphModule(torch.nn.Module):
        def forward(self, p_wrapped_module_wq_weight: "f32[2048, 2048]", p_wrapped_module_wk_weight: "f32[512, 2048]", p_wrapped_module_wv_weight: "f32[512, 2048]", p_wrapped_module_wo_weight: "f32[2048, 2048]", b_wrapped_module_kv_cache_k_cache: "f32[1, 2048, 8, 64]", b_wrapped_module_kv_cache_v_cache: "f32[1, 2048, 8, 64]", x: "f32[1, s27, 2048]", freqs_cos: "f32[s27, 32]", freqs_sin: "f32[s27, 32]", input_pos: "i64[1]"):
            sym_size: "Sym(s27)" = torch.ops.aten.sym_size.int(x, 1)

            ...

            # b_wrapped_module_kv_cache_*_cache are mutable buffers
            # getitem_2 and getitem_3 are derived from mutable buffers, hence they are
            # themselves mutable buffers
            auto_functionalized = torch.ops.higher_order.auto_functionalized(torch.ops.llama.update_cache.default, value = getitem_1, cache = b_wrapped_module_kv_cache_k_cache, start_pos = _local_scalar_dense_1);  getitem_1 = b_wrapped_module_kv_cache_k_cache = None
            getitem_2: "f32[1, 2048, 8, 64]" = auto_functionalized[1];  auto_functionalized = None
            auto_functionalized_1 = torch.ops.higher_order.auto_functionalized(torch.ops.llama.update_cache.default, value = aten_view_copy_default_8, cache = b_wrapped_module_kv_cache_v_cache, start_pos = _local_scalar_dense_1);  aten_view_copy_default_8 = b_wrapped_module_kv_cache_v_cache = _local_scalar_dense_1 = None
            getitem_3: "f32[1, 2048, 8, 64]" = auto_functionalized_1[1];  auto_functionalized_1 = None

            ...

            aten_permute_copy_default_3: "f32[2048, 2048]" = executorch_exir_dialects_edge__ops_aten_permute_copy_default(p_wrapped_module_wo_weight, [1, 0]);  p_wrapped_module_wo_weight = None
            aten_view_copy_default_10: "f32[s27, 2048]" = executorch_exir_dialects_edge__ops_aten_view_copy_default(aten_view_copy_default_9, [sym_size, 2048]);  aten_view_copy_default_9 = None
            aten_mm_default_3: "f32[s27, 2048]" = executorch_exir_dialects_edge__ops_aten_mm_default(aten_view_copy_default_10, aten_permute_copy_default_3);  aten_view_copy_default_10 = aten_permute_copy_default_3 = None
            aten_view_copy_default_11: "f32[1, s27, 2048]" = executorch_exir_dialects_edge__ops_aten_view_copy_default(aten_mm_default_3, [1, sym_size, 2048]);  aten_mm_default_3 = sym_size = None

            # getitem_2 and getitem_3 are returned as outputs, presumably to prevent the
            # update_cache calls from being removed due to dead code elimination
            return (getitem_2, getitem_3, aten_view_copy_default_11, None)
```

In the graph signature of the `ExportedProgram` these show up as `BUFFER_MUTATION` outputs

```
Graph signature:
    # inputs
    p_wrapped_module_wq_weight: PARAMETER target='wrapped_module.wq.weight'
    p_wrapped_module_wk_weight: PARAMETER target='wrapped_module.wk.weight'
    p_wrapped_module_wv_weight: PARAMETER target='wrapped_module.wv.weight'
    p_wrapped_module_wo_weight: PARAMETER target='wrapped_module.wo.weight'
    b_wrapped_module_kv_cache_k_cache: BUFFER target='wrapped_module.kv_cache.k_cache' persistent=True
    b_wrapped_module_kv_cache_v_cache: BUFFER target='wrapped_module.kv_cache.v_cache' persistent=True
    x: USER_INPUT
    freqs_cos: USER_INPUT
    freqs_sin: USER_INPUT
    input_pos: USER_INPUT

    # outputs
    getitem_2: BUFFER_MUTATION target='wrapped_module.kv_cache.k_cache'
    getitem_3: BUFFER_MUTATION target='wrapped_module.kv_cache.v_cache'
    aten_view_copy_default_11: USER_OUTPUT
    : USER_OUTPUT
```

Although these nodes are technically returned by the `fx.Graph`, `BUFFER_MUTATION` outputs are not included in the delegate call schema. Since the Vulkan delegate serialization uses the output node to mark which values are returned as outputs, this could result in a mismatch betwen the outputs of the Vulkan delegate and the outputs expected by the ExecuTorch runtime.

## Motivation

Previously, this mismatch was addressed in the runtime, by skipping the processing of non-tensor outputs. However, this solution does not account for the fact that in some models, paramters of the model may be returned as outputs. In this case, those parameter outputs would be skipped but the ExecuTorch runtime would still expect to receive them as outputs.

To solve the problem properly, this diff changes the serialization logic to check if an output node is a mutable buffer, and skip marking it as an output if so. In the runtime, all output nodes are processed instead of only processing tensor outputs.

Differential Revision: [D77281491](https://our.internmc.facebook.com/intern/diff/D77281491/)

ghstack-source-id: 292684341
Pull Request resolved: #11983

Author: SS-JIA

backends/vulkan/runtime/VulkanBackend.cpp

@@ -359,15 +359,11 @@ class GraphBuilder {
       vkFn(*compute_graph_, args);
     }
 
-    // Parse the outputs, which will be mostly tensors.  For some reason,
-    // mutable buffers are shown to be returned in the fx.Graph but do not get
-    // returned by the delegate; this may be an implementation detail of how the
-    // executorch emitter handles mutable buffers.
+    // Parse the outputs, which will be mostly tensors but may contain tensorref
+    // values as well if the source graph returns parameter nodes.
     for (const uint32_t fb_id : *flatbuffer_->output_ids()) {
       const ValueRef ref = get_fb_id_valueref(fb_id);
-      if (compute_graph_->val_is_tensor(ref)) {
-        compute_graph_->set_output_tensor(ref);
-      }
+      compute_graph_->set_output_value(ref);
     }
 
     if (compute_graph_->graphconfig().enable_querypool) {
@@ -609,6 +605,12 @@ class VulkanBackend final : public ::executorch::runtime::BackendInterface {
             compute_graph->outputs()[i].staging,
             args[o]->toTensor().mutable_data_ptr(),
             args[o]->toTensor().numel());
+      }
+      // TensorRef values represent constant tensors which will not have been
+      // modified by the graph execution. Therefore, if a constant tensor is
+      // returned as an output, no action is required.
+      else if (compute_graph->val_is_tref(oref)) {
+        continue;
       } else {
         VK_THROW(
             "Could not handle output with type ",

backends/vulkan/runtime/graph/ComputeGraph.cpp

@@ -519,6 +519,14 @@ ValueRef ComputeGraph::set_output_tensor(
   return idx;
 }
 
+ValueRef ComputeGraph::set_output_value(const ValueRef idx) {
+  if (values_.at(idx).isTensor()) {
+    return set_output_tensor(idx);
+  }
+  outputs_.push_back({idx, kDummyValueRef});
+  return idx;
+}
+
 vkapi::BufferBindInfo ComputeGraph::get_or_create_int_param_buffer(
     const ValueRef idx) {
   if (values_.at(idx).isInt()) {

backends/vulkan/runtime/graph/ComputeGraph.h

@@ -658,6 +658,8 @@ class ComputeGraph final {
   ValueRef set_input_tensor(const ValueRef idx, const bool use_staging = true);
   ValueRef set_output_tensor(const ValueRef idx, const bool use_staging = true);
 
+  ValueRef set_output_value(const ValueRef idx);
+
   template <typename Block>
   vkapi::BufferBindInfo create_params_buffer(const Block& data) {
     param_ubos_.emplace_back(api::ParamsBuffer(context_.get(), data));

backends/vulkan/serialization/vulkan_graph_builder.py

@@ -20,6 +20,7 @@
 from executorch.backends.vulkan.utils import (
     is_constant,
     is_get_attr_node,
+    is_mutable_buffer_node,
     is_param_node,
     is_symint_node,
 )
@@ -382,6 +383,11 @@ def process_output_node(self, node: Node) -> None:
                     "the output node is being serialized before its corresponding "
                     "internal node which is not allowed."
                 )
+            # Mutable buffers outputs are not included as an output to the
+            # delegate call. Skip marking them as an output.
+            if is_mutable_buffer_node(out_node, self.program):
+                continue
+
             self.output_ids.append(self.node_to_value_ids[out_node])
 
     def process_node(self, node: Node, call_node_debug_hdl: int) -> None:

backends/vulkan/utils.py

@@ -84,6 +84,15 @@ def is_param_node(program: ExportedProgram, node: torch.fx.Node) -> bool:
     )
 
 
+def is_mutable_buffer_node(
+    node: torch.fx.Node, exported_program: ExportedProgram
+) -> bool:
+    if node.target not in exported_program.graph_signature.inputs_to_buffers:
+        return False
+    buf = exported_program.graph_signature.inputs_to_buffers[node.target]
+    return buf in exported_program.graph_signature.buffers_to_mutate.values()
+
+
 def is_symint_node(node: torch.fx.Node) -> bool:
     """
     Returns true if the given node produces a SymInt value